Heretofore, variable chokes, i.e., fluid flow regulating means, have been employed in flow lines leading from wells such as oil and/or gas wells in the earth. These well flow line chokes have a movable means therein for varying the amount of restriction to be imposed by the choke on the well fluids flowing therethrough. Normally, the movable means in the choke body is designed to mate with an insert which is fixed in the body of the choke to thereby cause the choking (restricting) effect on the fluids passing therethrough. As will be shown in greater detail hereinafter, the insert means used in the prior art devices was disposed wholly within the body of the choke and either a section of pipe and valve means or the valve means itself was employed immediately downstream the fluid outlet end of the choke. For sake of simplicity only, this invention will be described hereinafter with the valve means being disposed immediately downstream of the choke. It should be understood that this will not always be the practice in the field. However, the benefits of this invention are realized whether a valve or a pipe section immediately follows the choke.
It has been discovered that, because of the pressure changes caused by the choking action, a blast effect is sometimes created which causes a highly turbulent atmosphere that can lead to substantial erosion of the internal surfaces of the body of the choke and the downstream pipe or valve means which, if left unchanged for a substantial period of time, can severely weaken the containing walls of the choke, downstream pipe, and/or downstream valve means.
Because of the construction of the choke and the mounting of the valve means closely to or directly to the choke, inspection for internal corrosion or erosion can be quite difficult and replacement of one or both of these parts of the flow line assembly quite expensive.